EFFECT OF REELING ON FATIGUE CRACK GROWTH BEHAVIOR OF WELDED API5LX65 LINE PIPE

摘要

The effect of reeling on the fatigue crack growth rate (FCGR) behavior of welded pipe was investigated both in-air as well as in sour environment. The FCGR behavior of the reeled pipe in various notch locations parent pipe (PP), weld center line (WCL), heat affected zone (HAZ) did not exhibit any effect of reeling (i.e. the properties in the strained and aged condition was similar to the as-fabricated welds). Frequency scan FCGR tests in sour environment (pH = 5/0.46psia H_2S) exhibited maximum KDF's in the range of 10x to 35x at frequencies in0 the range of 3mHz to 1mHz and 3x to 5x at frequencies in the range of 0.3Hz (Risers). In sour service WCL exhibited better fatigue performance than the parent pipe and HAZ in all conditions. Fatigue performance of parent pipe and WCL was independent of reeling. The poorest fatigue performance was observed in unstrained HAZ. Fatigue performance of HAZ extrados and intrados were similar and better than unstrained HAZ. It was also found that the FCGR in sour environments was controlled by the internal hydrogen due to bulk charging from the sour environment. The overall conclusion is that, reeling has no detrimental effect on sour service fatigue crack growth behavior i.e. sour service fatigue performance of reeled pipe is the same as unreeled pipe.